add functionality for handling error messages

Author: yucongalicechen

src/diffpy/utils/scattering_objects/diffraction_objects.py

@@ -17,6 +17,23 @@
     "and specifying how to handle the mismatch."
 )
 
+wavelength_warning_emsg = (
+    "INFO: no wavelength has been specified. You can continue "
+    "to use the DiffractionObject but some of its powerful features "
+    "will not be available. To specify a wavelength, set "
+    "diffraction_object.wavelength = [number], "
+    "where diffraction_object is the variable name of you Diffraction Object, "
+    "and number is the wavelength in angstroms."
+)
+
+length_mismatch_emsg = "Please ensure {array_name} array and intensity array are of the same length."
+non_numeric_value_emsg = "Invalid value found in {array_name} array. Please ensure all values are numeric."
+invalid_tth_emsg = "Two theta exceeds 180 degrees. Please check the input values for errors."
+invalid_q_or_wavelength_emsg = (
+    "The supplied q-array and wavelength will result in an impossible two-theta. "
+    "Please check these values and re-instantiate the DiffractionObject with correct values."
+)
+
 
 class Diffraction_object:
     """A class to represent and manipulate data associated with diffraction experiments.
@@ -778,12 +795,20 @@ def q_to_tth(self):
         two_theta : array
             The array of :math:`2\theta` values in radians
         """
+        for i, value in enumerate(self.on_q[0]):
+            if not isinstance(value, (int, float)):
+                raise TypeError(non_numeric_value_emsg.format(array_name="q"))
+        if len(self.on_q[0]) != len(self.on_q[1]):
+            raise RuntimeError(length_mismatch_emsg.format(array_name="q"))
+        if self.wavelength is None:
+            warnings.warn(wavelength_warning_emsg, UserWarning)
+            return np.empty(0)
         q = self.on_q[0]
         q = np.asarray(q)
         wavelength = float(self.wavelength)
         pre_factor = wavelength / (4 * np.pi)
         if np.any(np.abs(q * pre_factor) > 1):
-            raise ValueError("Please check if you entered an incorrect wavelength or q value.")
+            raise ValueError(invalid_q_or_wavelength_emsg)
         return np.rad2deg(2.0 * np.arcsin(q * pre_factor))
 
     def tth_to_q(self):
@@ -818,12 +843,17 @@ def tth_to_q(self):
             The array of :math:`q` values in the inverse of the units
             of ``wavelength``
         """
+        for i, value in enumerate(self.on_tth[0]):
+            if not isinstance(value, (int, float)):
+                raise TypeError(non_numeric_value_emsg.format(array_name="two theta"))
+        if len(self.on_tth[0]) != len(self.on_tth[1]):
+            raise RuntimeError(length_mismatch_emsg.format(array_name="two theta"))
         two_theta = np.asarray(np.deg2rad(self.on_tth[0]))
         if np.any(two_theta > np.pi):
-            raise ValueError(
-                "Two theta exceeds 180 degrees. Please check if invalid values were entered "
-                "or if degrees were incorrectly specified as radians."
-            )
+            raise ValueError(invalid_tth_emsg)
+        if self.wavelength is None:
+            warnings.warn(wavelength_warning_emsg, UserWarning)
+            return np.empty(0)
         wavelength = float(self.wavelength)
         pre_factor = (4 * np.pi) / wavelength
         return pre_factor * np.sin(two_theta / 2)

tests/diffpy/utils/scattering_objects/test_diffraction_objects.py

@@ -4,7 +4,7 @@
 import pytest
 from freezegun import freeze_time
 
-from diffpy.utils.scattering_objects.diffraction_objects import DiffractionObject
+from diffpy.utils.scattering_objects.diffraction_objects import DiffractionObject, wavelength_warning_emsg
 
 params = [
     (  # Default
@@ -238,35 +238,18 @@ def _test_valid_diffraction_objects(actual_diffraction_object, function, expecte
     if actual_diffraction_object.wavelength is None:
         with pytest.warns(UserWarning) as warn_record:
             getattr(actual_diffraction_object, function)()
-        assert str(warn_record[0].message) == (
-            "INFO: no wavelength has been specified. You can continue "
-            "to use the DiffractionObject but some of its powerful features "
-            "will not be available. To specify a wavelength, set "
-            "diffraction_object.wavelength = [number], "
-            "where diffraction_object is the variable name of you Diffraction Object, "
-            "and number is the wavelength in angstroms."
-        )
+        assert str(warn_record[0].message) == wavelength_warning_emsg
     actual_array = getattr(actual_diffraction_object, function)()
     return np.allclose(actual_array, expected_array)
 
 
 params_q_to_tth = [
     # UC1: User specified empty q values (without wavelength)
-    (
-        [None, [], []],
-        [[]],
-    ),
+    ([None, [], []], [[]]),
     # UC2: User specified empty q values (with wavelength)
-    (
-        [4 * np.pi, [], []],
-        [[]],
-    ),
+    ([4 * np.pi, [], []], [[]]),
     # UC3: User specified valid q values (without wavelength)
-    # expected tth values are 2*arcsin(q) in degrees
-    (
-        [None, [0, 0.2, 0.4, 0.6, 0.8, 1], [1, 2, 3, 4, 5, 6]],
-        [[]],
-    ),
+    ([None, [0, 0.2, 0.4, 0.6, 0.8, 1], [1, 2, 3, 4, 5, 6]], [[]]),
     # UC4: User specified valid q values (with wavelength)
     # expected tth values are 2*arcsin(q) in degrees
     (
@@ -300,18 +283,18 @@ def test_q_to_tth(inputs, expected):
         [
             ValueError,
             "The supplied q-array and wavelength will result in an impossible two-theta. "
-            "Please check these values and re-instantiate the DiffractionObject.",
+            "Please check these values and re-instantiate the DiffractionObject with correct values.",
         ],
     ),
     # UC3: user specified a q array that does not match the length of intensity array (without wavelength)
     (
         [None, [0, 0.2, 0.4, 0.6, 0.8, 1], [1, 2, 3, 4, 5]],
-        [RuntimeError, "Please ensure q array and intensity array are the same length."],
+        [RuntimeError, "Please ensure q array and intensity array are of the same length."],
     ),
     # UC4: user specified a q array that does not match the length of intensity array (with wavelength)
     (
         [4 * np.pi, [0, 0.2, 0.4, 0.6, 0.8, 1], [1, 2, 3, 4, 5]],
-        [RuntimeError, "Please ensure q array and intensity array are the same length."],
+        [RuntimeError, "Please ensure q array and intensity array are of the same length."],
     ),
     # UC5: user specified a non-numeric value in q array (without wavelength)
     (
@@ -336,26 +319,17 @@ def test_q_to_tth_bad(inputs, expected):
 
 params_tth_to_q = [
     # UC1: User specified empty tth values (without wavelength)
-    (
-        [None, [], []],
-        [[]],
-    ),
+    ([None, [], []], [[]]),
     # UC2: User specified empty tth values (with wavelength)
-    (
-        [4 * np.pi, [], []],
-        [[]],
-    ),
+    ([4 * np.pi, [], []], [[]]),
     # UC3: User specified valid tth values between 0-180 degrees (without wavelength)
     (
         [None, [0, 30, 60, 90, 120, 180], [1, 2, 3, 4, 5, 6]],
         [[]],
     ),
     # UC4: User specified valid tth values between 0-180 degrees (with wavelength)
     # expected q vales are sin15, sin30, sin45, sin60, sin90
-    (
-        [4 * np.pi, [0, 30, 60, 90, 120, 180], [1, 2, 3, 4, 5, 6]],
-        [[0, 0.258819, 0.5, 0.707107, 0.866025, 1]],
-    ),
+    ([4 * np.pi, [0, 30, 60, 90, 120, 180], [1, 2, 3, 4, 5, 6]], [[0, 0.258819, 0.5, 0.707107, 0.866025, 1]]),
 ]
 
 
@@ -381,12 +355,12 @@ def test_tth_to_q(inputs, expected):
     # UC3: user specified a two theta array that does not match the length of intensity array (without wavelength)
     (
         [None, [0, 30, 60, 90, 120], [1, 2, 3, 4, 5, 6]],
-        [RuntimeError, "Please ensure two theta array and intensity array are the same length."],
+        [RuntimeError, "Please ensure two theta array and intensity array are of the same length."],
     ),
     # UC4: user specified a two theta array that does not match the length of intensity array (with wavelength)
     (
         [4 * np.pi, [0, 30, 60, 90, 120], [1, 2, 3, 4, 5, 6]],
-        [RuntimeError, "Please ensure two theta array and intensity array are the same length."],
+        [RuntimeError, "Please ensure two theta array and intensity array are of the same length."],
     ),
     # UC5: user specified a non-numeric value in two theta array (without wavelength)
     (